Flower Growth, Anthocyanin Accumulation And CHS,DFR Gene Expression Regulated By Light In Gerbera Hybrida

After floral initiation and organ identity, the late developmental stage including flower growth and pigmentation is a key process contributing to the commercial characteristics of ornamental flowers. It is clear that the growth and anthocyanin accumulation in flower petals are regulated by environmental and developmental signals in which light is the most important environmental cue. In the present study, the changes of flower growth and anthocyanin accumulation and their photoregulation were investigated in Gerbera hybrida, one of the most popular five cut flowers in the world. In Gerbera, more than one morphological flower type exist in a single head-like inflorescence with many parameters varying in a single genotype, offering a unique model system in Asteraceae for studying inflorescence and flower development.Basing on our description of the six stages (P1-P6) of inflorescence development in Gerbera hybrida, in vitro experimental system was established to culture detached inflorescences and ray floret (rf). We compared the changes of flower growth, anthocyanin accumulation and CHS, DFR gene expression in vivo and in vitro and investigated the effect of light on flower growth and pigmentation. Additionally, the roles of sugar and GA3 in the process were also discussed. The major results are as follows:1. During inflorescence development, anthocyanin accumulation of rf petal coincided with the growth of the inflorescences and rfs in vivo. The fresh weight and size of inflorescences reached the maximum when flower was fully opened at P6, while pigmentation reached the highest level when inflorescence was half opened (P5). Changes of CHS and DFR gene expression were similar to that of anthocyanin accumulation during inflorescence development.2. Inflorescences and rfs were detached at the P2 and incubated on the sucrose medium (8 g/L agar with 3% sucrose), respectively. They could grow and accumulate anthocyanin on the medium during the culture time. However, the maximum level of the growth and pigmentation in vitro were lower than those in vivo. Sugar was required for detachedflower growth and pigmentation in vitro. Among various sugars tested, the metabolic sugars including sucrose, glucose and fructose showed effective in anthocyanin accumulation, while non-metabolic mannitol and sorbitol had no effect on pigmentation.3. When inflorescences were shaded with aluminum foil in vivo at the early developmental P1 and P2, anthocyanin accumulation and flower growth were dramatically inhibited; This inhibition could not be reversed when the shading was removed and the inflorescences were re-exposed to light at late stages. Our results demonstrated that light plays the key roles in flower growth and pigmentation only in the early stages of Gerbera flower development and it has a little role at the later developmental stages. Similar results in anthocyanin accumulation were obtained when inflorescences and rfs were cultured in vitro. There was a close relationship between light-regulated anthocyanin accumulation and flower growth in vivo and they had no significant correlation in vitro.4. When inflorescences were re-exposed to light at the P3 after shading at P1, the gene expression was down-regulated. Transient light exposure could induce CHS and DFR gene expression of rf petal when the inflorescences were cultured in vitro and the level of anthocyanin accumulation increased with the culture time after light treatment. The light induction of the gene expression decreased gradually when the pre-dark culture time was longer than 3 d. Our data demonstrated that there was an appropriate developmental time of the inflorescences responding to photoregulation of the anthocyanin accumulation both in vivo and in vitro.5. The ultrastructure of the plastids in rf petals were examined. Normal and intact chloroplasts were found in the P1 and P2 of flower development. They began to deteriorate at P3 and declined into chromoplast-like structure at P6; Similar results were obtained from inflorescences shaded...